Bandpass filters based on integrated aperture‐ and gap‐coupled discontinuities

Abstract

An electromagnetic coupling mechanism is discussed for distributed-element aperture- and gap-coupled discontinuities based on rigorous lumped-element equivalent circuit analysis. The two discontinuities are analysed in terms of their transmission poles and transmission zeros for the selectivity enhancement of microwave and or millimetre-wave components. The integration of these two discontinuities is put forward for bandpass filter design. A frequency-dependent lumped-element equivalent circuit is employed to study the behaviour of the two distributed-element discontinuities in the transverse direction. Bandpass filters are characterised based on the dual aperture- and gap-coupled discontinuities integrated within substrate integrated waveguide structures. It is shown that multiple transmission zeros close to transmission poles are realised due to the magnetic and electric field cancelation in the gap-coupled discontinuity, while the aperture-coupled discontinuity contributes to a resonator with a higher quality factor. The integration of both aperture- and gap-coupled discontinuities shows the priority of this kind of microwave resonator in terms of selectivity, size, and upper stopband in comparison with the conventional aperture-coupled one.